Whereas intercommunicating subscribers of a telegraph or teleprinter system generally know each other's identity upon the establishment of a signal path therebetween, such is not the case in the usual telephone system where, with more conventional exchanges, the identity of a caller is not known beyond the subscriber's cord. Even with an automatic exchange operating under the control of a processor, e.g. with pulse-code modulation, the processor does not preserve the call numbers of the participating subscriber stations beyond the termination of a talking connection; while the identity of a station making a long-distance call may be recorded for billing purposes, extracting that information from the metering devices is a cumbersome task. There are, however, a number of instances when an instantaneous identification of a subscriber station participating in a talking connection would be useful to an operator at the exchange or to a participating subscriber. Thus, for example, the operator may recognize a particular caller as entitled to or barred from certain services. A calling party could ascertain whether or not the correct station has been reached when, say, the called subscriber does not respond. Conversely, a subscriber receiving a malicious call would be able to trace its origin immediately. The metering and documentation of trunk calls could also be simplification with the aid of equipment adapted to identify calling and called stations at any time in the course of a conversation. Such equipment would further facilitate the monitoring of traffic over a particular line, including the recording of abortive calls.